Refrigeration air dryer

ABSTRACT

A refrigeration air dryer outputs dehumidified air dehumidified by a cooling operation using a low-temperature refrigerant after the temperature thereof has been raised by exchanging heat with a high-temperature refrigerant at a reheater. The refrigeration air dryer includes a temperature sensor which detects the temperature of secondary air in the outlet pipe, valve means which adjusts the flow rate of the dehumidified air or the flow rate of the refrigerant flowing through the reheater, and a temperature controller which adjusts the flow rate of the dehumidified air or the flow rate of the refrigerant by controlling the valve means based upon the detected temperature detected by the temperature sensor, thereby maintaining the temperature of the secondary air at a constant level.

BACKGROUND OF THE INVENTION

[1] Field of the Invention

The present invention relates to a refrigeration air dryer which dehumidifies compressed air by condensing the moisture in the compressed air by cooling the compressed air.

[2] Description of the Related Art

In air compressor system employing solenoid valves, air cylinders, etc., in order to prevent trouble from occurring due to the moisture included in compressed air to be supplied to the air compressor system, the moisture included in the compressed air is preferably removed beforehand. In order to remove such moisture, a refrigeration air dryer is employed. Such a refrigeration air dryer preferably controls the temperature of the compressed air at the outlet of the air dryer so as to again raise the temperature of the dehumidified compressed air in order to prevent occurrence of dew condensation at the secondary air pipe in the air dryer due to low-temperature compressed air dehumidified by cooling.

FIG. 3 shows a circuit of a refrigerant system and an air system in a conventional refrigeration air dryer which is capable of controlling the temperature of the compressed air at the outlet of the air dryer. The refrigeration system in the refrigeration air dryer includes a refrigerant compressor 10, a condenser 11 which condenses the high-temperature refrigerant compressed by the refrigerant compressor 10 and transmitted via a high-temperature refrigerant pipe 22, an expansion valve 12 which decompresses, by adiabatic expansion, the refrigerant thus condensed by the condenser 11 so as to lower the temperature of the refrigerant, and a cooler 13 which cools the moist compressed air, which has been input via the air inlet 20 of the air system, using the low-temperature refrigerant transmitted from the expansion valve 12, so as to dehumidify the air. The refrigerant system is configured such that the refrigerant from the cooler 13 is returned to the refrigerant compressor 10 via a return refrigerant pipe 26.

On the other hand, the aforementioned air system has a configuration in which, after the moist compressed air (primary air) input from the exterior via the air inlet 20 is cooled by the cooler 13, drain separation processing is performed by a drain separator 16 so as to provide low-temperature dehumidified air, the dehumidified air is reheated by an electric heater 14, and the dehumidified air thus reheated is transmitted as secondary air to an outlet pipe 21. With such an arrangement, a temperature sensor 40 is provided to the outlet pipe 21. The temperature of the secondary air detected by the temperature sensor 40 is input to a temperature controller 41, and the temperature controller 41 controls the output of the electric heater 14, thereby controlling the temperature of the secondary air at the outlet of the air dryer. Such an arrangement provides temperature control operation with relatively high precision. It should be noted that the drain separator 16, which performs the aforementioned drain separation processing, includes a drain valve 15 which externally discharges resultant water drops.

In such a conventional refrigeration air dryer, the low-temperature dehumidified air, which has been dehumidified by cooling, is reheated by the electric heater 14. Accordingly, such a conventional refrigeration air dryer requires great electric power, approximately the same as with the refrigerator. Accordingly, although the aforementioned conventional refrigeration air dryer is capable of controlling the temperature with high precision, such an arrangement has the disadvantage of great electric power consumption.

On the other hand, a technique has been known in which, instead of the electric heater 14, a reheater is provided which exchanges heat between the warm primary air input via the air inlet 20 and the low-temperature dehumidified air transmitted via the cooler 13, using the difference in temperature therebetween. With such an arrangement, by exchanging heat as described above, the primary air is preliminarily cooled, and the temperature of the dehumidified air is raised, following which the dehumidified air thus heated is output as secondary air. With such an arrangement including such a reheater, the primary air is preliminarily cooled, following which the primary air thus preliminarily cooled is again cooled by the cooler, thereby reducing the load to be applied to the refrigeration circuit. Furthermore, such an arrangement prevents occurrence of dew condensation at an air pipe by raising the temperature of the secondary air transmitted from the air dryer. Thus, such an arrangement effectively uses thermal energy. However, the temperature of the secondary air is dependent upon the temperature of the primary air. In a case in which the temperature of the primary air input via the air inlet 20 is low, in some cases, the secondary air discharged from the outlet pipe 21 cannot be raised up to a temperature at which dew condensation at the outlet pipe 21 can be prevented. It is difficult for such an arrangement to stably maintain the temperature in a required temperature range.

It should be noted that, in the aforementioned conventional refrigeration air dryer, in general, the temperature of the high-temperature refrigerant flowing into the condenser 11 from the refrigerant compressor 10 via the high-temperature refrigerant pipe 22 is approximately 90° C. On the other hand, the temperature of the low-temperature refrigerant, which flows into the cooler 13 via the low-temperature refrigerant pipe 23 after the adiabatic expansion provided by the expansion valve 12, is approximately 5° C. Furthermore, the temperature of the primary air, which is input via the air inlet 20, is 40° C. (rated temperature). The temperature of the dehumidified air transmitted from the cooler 13 to the electric heater 14 via the drain separator 16 is approximately 10° C.

It should be noted that, in the refrigeration air dryer, the high-temperature refrigerant pipe 22 that connects the refrigerant compressor 10 and the condenser 11 and the low-temperature refrigerant pipe 23 that connects the expansion valve 12 and the cooler 13 communicate with each other via a bypass refrigerant pipe 25 including a volume adjusting valve 17 which provides an adjustable aperture. As described above, the bypass refrigerant pipe 25 is provided in order to mix a portion of the refrigerant, which flows from the refrigerant compressor 10 to the condenser 11, into the refrigerant flowing through the cooler 13, so as to prevent the moisture included in the primary air flowing from the air inlet 20 to the cooler 13 from freezing due to excessive reduction in the temperature of the refrigerant flowing through the cooler 13.

BRIEF SUMMARY OF INVENTION

It is a technical object of the present invention to provide a refrigeration air dryer which is capable of controlling the temperature of the secondary air in the outlet pipe with high precision as with an arrangement employing an electric heater, using a reheater employing heat occurring in the refrigerant system to raise the temperature of the secondary compressed air, by adjusting the flow rate of the refrigerant or air flowing through the reheater, without a need to heat the secondary air in the outlet pipe using an electric heater unlike the aforementioned conventional refrigeration air dryer.

In order to solve the aforementioned problem, a refrigeration air dryer is provided including: a refrigerant system which includes a refrigerant compressor, a condenser which condenses a high-temperature refrigerant compressed by the refrigerant compressor, a decompressing mechanism which decompresses, by adiabatic expansion, the refrigerant which has been condensed by the condenser, so as to lower the temperature thereof, and a cooler which cools moist compressed air input via the air inlet in an air system, using the low-temperature refrigerant transmitted from the decompressing mechanism, so as to dehumidify the air, and which is configured such that the refrigerant transmitted from the cooler is returned to the refrigerant compressor; and the air system which includes the air inlet which allows moist compressed air, which is input as primary air to be dehumidified, the cooler which cools the primary air input via the air inlet so as to obtain low-temperature dehumidified air, and a reheater which exchange heat between the low-temperature dehumidified air transmitted from the cooler and the high-temperature refrigerant transmitted from the refrigerant compressor included in the refrigerant system, and which outputs the dehumidified air, of which the temperature has been raised by the heat exchange at the reheater, is output as secondary air via the outlet pipe. With such an arrangement, the air dryer includes a temperature sensor which detects the temperature of the secondary air flowing through the outlet pipe, valve means which adjusts the flow rate of the dehumidified air or the refrigerant flowing through the reheater, and a temperature controller which adjusts the flow rate of the dehumidified air or the refrigerant by controlling the valve means based upon the detected temperature detected by the temperature sensor, so as to maintain the temperature of the secondary air at a constant level.

The air dryer according to the present invention is preferably configured such that the reheater is connected between the refrigerant compressor and the condenser, and the refrigerant transmitted from the refrigerant compressor is transmitted to the condenser via the reheater.

Also, an arrangement may be made in which a high-temperature refrigerant pipe which connects the refrigerant compressor and the reheater and a low-temperature refrigerant pipe which connects the decompressing mechanism and the cooler or a return refrigerant pipe which connects the cooler and the refrigerant compressor are connected such that they communicate with each other via a bypass refrigerant pipe including a volume adjusting valve which provides an adjustable aperture, thereby allowing a portion of the high-temperature refrigerant compressed by the refrigerant compressor to directly flow through the low-temperature refrigerant pipe or the return refrigerant pipe in a case in which the load of the cooler has become small.

With the present invention, the valve means preferably comprises a three-way flow adjusting valve having one inlet port and two outlet ports. With such an arrangement, the three-way flow adjusting valve preferably allows a portion of the dehumidified air or the refrigerant, which is to be transmitted to the reheater, to flow bypassing the reheater.

In this case, also, an arrangement may be made in which a bypass pipe that bypasses the reheater is connected to the dehumidified air pipe which transmits the dehumidified air from the cooler to the reheater and the outlet pipe which outputs the secondary air transmitted from the reheater, and the three-way flow adjusting valve is arranged at a branching node at which the bypass pipe is provided branching from the dehumidified air pipe or at a junction of the bypass pipe and the outlet pipe.

Also, an arrangement may be made in which a refrigeration bypass pipe that bypasses the reheater is connected to a high-temperature refrigerant pipe which connects the refrigerant compressor and the reheater and an intermediate refrigerant pipe which connects the reheater and the condenser, and the three-way flow adjusting valve is arranged at a branching node at which the refrigeration bypass pipe is provided branching from the high-temperature refrigerant pipe or at a junction of the refrigerant bypass pipe and the intermediate refrigerant pipe.

With the refrigeration air dryer according to the present invention having the above-described configuration, the flow rate of the dehumidified air to be transmitted to the reheater after drain separation processing, or the flow rate of the refrigerant from the refrigerant compressor is controlled based upon the temperature of the dehumidified air flowing through the outlet pipe such that the temperature thereof is maintained at a constant level. Accordingly, the refrigeration air dryer is capable of controlling the flow rate thereof with relatively high precision using electric means. Thus, the refrigeration air dryer employing such a reheater is capable of controlling the temperature of the compressed air in the outlet pipe with high precision as with an arrangement employing an electric heater.

The above-described refrigeration air dryer according to the present invention employs the reheater to use heat that occurs in the refrigerant system to raise the temperature of the compressed air at the outlet pipe, instead of employing an electric heater to heat the dehumidified air at the outlet pipe, unlike the aforementioned conventional refrigeration air dryers. By adjusting the flow rate of the fluid that flows through the reheater, such an arrangement controls the temperature of the compressed air at the outlet pipe with high precision as with an arrangement employing an electric heater.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram which shows a refrigeration system and an air system of a refrigeration air dryer according to a first embodiment of the present invention.

FIG. 2 is a similar circuit diagram which shows a refrigeration air dryer according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram which shows a refrigeration system and an air system of a conventional refrigeration air dryer.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a first embodiment of a refrigeration air dryer according to the present embodiment, and FIG. 2 shows a second embodiment of a refrigeration air dryer according to the present embodiment. In these embodiments, the same components as those of a conventional refrigeration air dryer shown in FIG. 3 are denoted by the same reference numerals shown in FIG. 3.

Roughly, the refrigeration air dryer according to the first embodiment shown in FIG. 1 includes a refrigerant system, an air system, and a control system which controls the flow rate of dehumidified air or the flow rate of a refrigerant flowing through a reheater 18 connected to the refrigerant system and the air system, so as to maintain the temperature of the secondary air output from the refrigeration air dryer.

The aforementioned refrigerant system includes: a refrigerant compressor 10; a high-temperature refrigerant pipe 22 which transmits a refrigerant, which has been compressed by the refrigerant compressor 10 so as to have a high temperature, to the reheater 18; a condenser 11 which condenses the refrigerant transmitted from the reheater 18 via an intermediate refrigerant pipe 27; an expansion valve 12 which decompresses, by adiabatic expansion, the refrigerant thus condensed by the condenser 11 so as to lower the temperature of the refrigerant; and a cooler 13 which cools the moist compressed air, which has been input via the air inlet 20 of the air system, using the low-temperature refrigerant transmitted from the expansion valve 12. The refrigerant system is configured such that the refrigerant transmitted from the cooler 13 is returned to the refrigerant compressor 10 via a return refrigerant pipe 26.

It should be noted that the expansion valve 12 has been illustrated as an example of the decompressing mechanism. Also, capillary tubes or the like may be employed instead of the expansion valve, for example.

On the other hand, the air system of the refrigeration air dryer includes: an air inlet 20 via which warm and moist compressed air (with rated temperature of 40° C.) to be dehumidified is input as primary air from the exterior: the cooler 13 which condenses the moisture by cooling the primary air input via the air inlet 20: a drain separator 16 which dehumidifies the compressed air, which has been cooled by the cooler 13, by performing drain separation processing: and the reheater 18 which exchanges heat between the low-temperature dehumidified air thus subjected to drain separation processing by the drain separator 16 and the high-temperature refrigerant compressed by the refrigerant compressor 10 included in the refrigerant system. The air system is configured such that the temperature of the low-temperature dehumidified air is raised by the heat exchange operation at the reheater 18, and the dehumidified air with a raised temperature is transmitted as secondary air to the outlet pipe 21.

Accordingly, the aforementioned cooler 13 and the reheater 18 are connected to both the refrigerant system and the air system, and functionally connect the refrigerant system and the air system.

It should be noted that the drain separator 16, which performs the aforementioned drain separation processing, includes a drain valve 15 which externally discharges resultant water drops.

The aforementioned control system, which maintains the temperature of the secondary air flowing through the outlet pipe 21, includes a three-way flow adjusting valve 30 connected in a dehumidified air pipe 28 that connects the drain separator 16 and the reheater 18. The three-way flow adjusting valve 30 has one inlet port 30 a and two outlet ports 30 b and 30 c, and is configured such that the dehumidified air input via the inlet port 30 a is distributed and the dehumidified air thus distributed is output from two outlet ports 30 b and 30 c. The inlet port 30 a is connected to an upstream portion 28 a of the dehumidified air pipe 28 which communicates with the drain separator 16. The outlet port 30 b, which is one of the outlet ports, is connected to a downstream portion 28 b of the dehumidified an pipe 28 which communicates with the reheater 18. A bypass pipe 29 is connected between the branching outlet port 30 c and the outlet pipe 21.

The bypass pipe 29 allows a portion of the dehumidified air flowing through the dehumidified air pipe 28 to bypass the reheater 18, and to directly flow toward the outlet side of the reheater 18. The bypass pipe 29 allows the flow rate of the dehumidified air flowing through the reheater 18 to be adjusted.

Furthermore, the aforementioned control system includes a temperature sensor 40 which is connected to the outlet pipe 21, and which detects the temperature of the secondary air flowing through the outlet pipe 21. The temperature sensor 40 and the three-way flow adjusting valve 30 are connected to a temperature controller 42. The temperature controller 42 controls the three-way flow adjusting valve 30 based upon the detected temperature of the secondary air thus detected by the temperature sensor 40, thereby controlling the flow rates of the dehumidified air passing through the reheater 18 and of the dehumidified air bypassing the reheater 18.

The temperature controller 42 makes a comparison between the temperature target value set beforehand and the actual detected temperature thus detected by the temperature sensor 40, and controls the aperture of the three-way flow adjusting valve 30 such that the difference therebetween becomes zero, i.e., so as to maintain the temperature of the secondary air in the outlet pipe 21 thereby controlling the flow rate of the dehumidified air flowing the bypass pipe 29 and the flow rate of the dehumidified air flowing through the reheater 18.

It should be noted that the three-way flow adjusting valve 30 is not restricted to a single valve. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air flowing through the bypass pipe 31 and the flow rate of the dehumidified air flowing through the reheater 18 based upon a signal received from the temperature controller 42.

By detecting the temperature of the secondary air flowing through the outlet pipe 21 by the temperature sensor 40, and by controlling the flow rate of the dehumidified air flowing through the bypass pipe 29 and the flow rate of the dehumidified air flowing through the reheater 18 based upon the temperature thus detected, the refrigeration air dryer having such a configuration according to the first embodiment is capable of controlling the temperature of the secondary air output via the outlet pipe 21 using the reheater 18 with high precision as with a conventional arrangement employing an electric heater.

Next, in comparison with the above-described first embodiment, description will be made regarding a refrigeration air dryer according to a second embodiment of the present invention with reference to FIG. 2. In the refrigerant system according to the second embodiment, a three-way flow adjusting valve 32, which is controlled by the temperature controller 42, is provided within the high-temperature refrigerant pipe 22 that connects the refrigerant compressor 10 and the reheater 18. The three-way flow adjusting valve 32 is the same as that employed in the above-described first embodiment, and has one inlet port 32 a and two outlet ports 32 b and 32 c. The inlet port 32 a is connected to an upstream portion 22 a of the high-temperature refrigerant pipe 22 which communicates with the refrigerant compressor 10. The outlet port 32 b, which is one of the outlet ports, is connected to a downstream portion 22 b of the high-temperature refrigerant pipe 22 which communicates with the reheater 18, and the other outlet port 32 c, which is a branching port, is connected to one terminal of the refrigerant bypass pipe 31. The other terminal of the refrigerant bypass pipe 31 is connected to the intermediate refrigerant pipe 27 which connects the outlet of the reheater 18 and the condenser 11. The refrigerant bypass pipe 31 allows a portion of the refrigerant flowing through the high-temperature refrigerant pipe 22 to bypass the reheater 18, and to directly flow toward the outlet side of the reheater 18.

The other configurations of the refrigeration air dryer according to the second embodiment are substantially the same as those of the refrigeration air dryer according to the first embodiment. Accordingly, description of such common configurations will be omitted.

The three-way adjusting valve 32 is controlled by the temperature controller 42 such that the temperature of the secondary air in the outlet pipe 21 detected by the temperature sensor 40 equals the target value set for the temperature controller 42. This control operation is substantially the same as the control operation of the three-way flow adjusting valve 30 according to the first embodiment.

The three-way flow adjusting valve 32 according to the second embodiment is not restricted to a single valve, as with the three-way flow adjusting valve 30 according to the first embodiment. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air flowing through the bypass pipe 31 and the flow rate of the dehumidified air flowing through the reheater 18 based upon a signal received from the temperature controller 42.

On the other hand, the air system according to the second embodiment is configured such that all of the low-temperature dehumidified air subjected to drain separation processing by the drain separator 16 is transmitted to the reheater 18 via the dehumidified air pipe 28, unlike the air system of the refrigeration air dryer according to the first embodiment. However, the other configurations except for this difference are substantially the same as those of the refrigeration air dryer according to the first embodiment.

With the second embodiment, as described above, by providing the three-way adjusting valve 32 within the high-temperature refrigerant pipe 22 that connects the refrigerant compressor 10 and the reheater 18, and by controlling the flow rate of the high-temperature refrigerant flowing through the reheater 18, the temperature of the secondary air in the outlet pipe 21 detected by the temperature sensor 40 can be controlled such that it attains the target value set for the temperature controller 42, as with the first embodiment. It should be noted that, in FIG. 2 showing the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals.

In the first embodiment described above, the bypass pipe 29 is provided branching from the dehumidified air pipe 28 via which the dehumidified air flows into the reheater 18, and the three-way flow adjusting valve 30 is provided at a junction of these pipes 28 and 29. Also, instead of this junction, the three-way flow adjusting valve 30 may be arranged at a junction of the bypass pipe 29 and the outlet pipe 21.

On the other hand, in the above-described second embodiment, the refrigerant bypass pipe 31 is provided branching from the high-temperature refrigerant pipe 22 which transmits the refrigerant from the refrigerant compressor 10 to the reheater 18, and the three-way flow adjusting valve 32 is arranged at the junction thus formed. Also, instead of this junction, the three-way flow adjusting valve 32 may be arranged at the junction of the refrigerant bypass pipe 31 and the intermediate refrigerant pipe 27 arranged on the outlet side of the reheater 18.

It is needless to say that, in such modifications in which the three-way flow adjusting valve is arranged at such a pipe junction, the flow rate of the dehumidified air or the refrigerant flowing through the reheater 18 and the bypass pipe 29 or 31 is controlled according to a control signal received from the temperature controller 42.

The three-way flow adjusting valve arranged at the junction is not restricted to a single valve. Also, a combination of multiple valves may be employed as long as it is capable of controlling the flow rate of the dehumidified air or the refrigerant flowing through the reheater 18 and the bypass pipe 29 or 31 according to a control signal received from the temperature controller 42.

It should be noted that, in the above-described first and second embodiments, the high-temperature refrigerant pipe 22 that connects the refrigerant compressor 10 and the reheater 18 and the low-temperature refrigerant pipe 23 that connects the expansion valve 12 and the cooler 13 are connected so as to communicate with each other via the bypass refrigerant pipe 25 including the volume adjusting valve 17 which provides an adjustable aperture. The bypass refrigerant pipe 25 is provided in order to mix a portion of the high-temperature refrigerant transmitted from the refrigerant compressor 10 into the low-temperature refrigerant in the low-temperature refrigerant pipe 23, bypassing the reheater 18, the condenser 11, and the expansion valve 12, by instructing the volume adjusting valve 17 to provide a suitable aperture, so as to maintain the temperature of the low-temperature refrigerant such that it does not become equal to or smaller than a predetermined temperature, thereby preventing the moisture included in the moist primary air, which flows from the air inlet 20 to the cooler 13, from freezing due to excessive reduction in the temperature of the refrigerant flowing from the expansion valve 12 to the cooler 13 via the low-temperature refrigerant pipe 23, in a case in which the load of the cooler 13 has become small. Accordingly, the bypass refrigerant pipe 25 is a component which provides a function of adjusting the flow rate of the refrigerant flowing through the reheater 18, the condenser 11, and the expansion valve 12.

The bypass refrigerant pipe 25 may be connected to the high-temperature refrigerant pipe 22 and the return refrigerant pipe 26 that connects the cooler 13 and the refrigerant compressor 10. In this case, by reducing the flow of the refrigerant flowing through the cooler 13, such an arrangement provides the same advantage as with the above-described arrangement, i.e., the advantage of preventing the moisture included in the air cooled by the cooler 13 from freezing.

The temperature of the refrigerant or the compressed air at each component in the refrigerant system and the air system in the refrigeration air dryer according to the first and second embodiments as described above are almost the same as those in the conventional refrigeration air dryer shown in FIG. 3, except for the temperature of the secondary air at the outlet pipe 21. However, with each of the above-described embodiments, the temperature of the secondary air in the outlet pipe 21 is controlled, thereby providing stable temperature thereof. Furthermore, the flow rate of the dehumidified air which has been subjected to the drain separation processing and which is to be transmitted to the reheater 18, or the flow rate of the refrigerant from the refrigerant compressor 10 is controlled such that the temperature of the secondary air flowing through the outlet pipe 21 is maintained at a constant level based upon the temperature thereof. Thus, such an arrangement is capable of controlling the flow rate thereof with relatively high precision by electric means. Thus, such an arrangement employing the reheater 18 is capable of controlling the temperature of the secondary air in the outlet pipe 21 with high precision, as with an arrangement employing an electric heater. 

1. A refrigeration air dryer including: a refrigerant system which includes a refrigerant compressor, a condenser condensing a high-temperature refrigerant compressed by the refrigerant compressor, a decompressing mechanism decompressing, by adiabatic expansion, the refrigerant condensed by the condenser, so as to lower the temperature thereof, and a cooler cooling moist compressed air flowing into through an air inlet in an air system, using the low-temperature refrigerant transmitted from the decompressing mechanism, so as to dehumidify the air, and which is configured such that the refrigerant transmitted from the cooler is returned to the refrigerant compressor: and the air system which includes the air inlet into which moist compressed air flows as a primary air to be dehumidified, the cooler cooling the primary air flowed into from the air inlet so as to obtain low-temperature dehumidified air, and a reheater exchanging heat between the low-temperature dehumidified air transmitted from the cooler and the high-temperature refrigerant transmitted from the refrigerant compressor included in the refrigerant system, and which outputs the dehumidified air, of which the temperature raised by the heat exchange at the reheater, as secondary air via the outlet pipe, wherein the air dryer includes a temperature sensor detecting the temperature of the secondary air flowing through the outlet pipe, valve means adjusting the flow rate of the dehumidified air or the refrigerant flowing through the reheater, and a temperature controller adjusting the flow rate of the dehumidified air or the refrigerant by controlling the valve means based upon the detected temperature detected in the temperature sensor, so as to maintain the temperature of the secondary air at a constant level.
 2. A refrigeration air dryer according to claim 1, wherein the reheater is connected between the refrigerant compressor and the condenser, and wherein the refrigerant transmitted from the refrigerant compressor is transmitted to the condenser via the reheater.
 3. A refrigeration air dryer according to claim 2, wherein a high-temperature refrigerant pipe connecting the refrigerant compressor and the reheater and a low-temperature refrigerant pipe connecting the decompressing mechanism and the cooler or a return refrigerant pipe connecting the cooler and the refrigerant compressor are connected via a bypass refrigerant pipe including a volume adjusting valve with an adjustable ratio of valve opening, whereby a portion of the high-temperature refrigerant compressed by the refrigerant compressor is directly flowed through the low-temperature refrigerant pipe or the return refrigerant pipe, in a case in which the load of the cooler becomes small.
 4. A refrigeration air dryer according to any one of claim 1 through claim 3, wherein the valve means comprises a three-way flow adjusting valve having one inlet port and two outlet ports, and wherein a portion of the dehumidified air or the refrigerant transmitting to the reheater is flowed by the three-way flow adjusting valve so as to bypass the reheater.
 5. A refrigeration air dryer according to claim 4, wherein a bypass pipe bypassing the reheater is connected to the dehumidified air pipe which transmits the dehumidified air from the cooler to the reheater and the outlet pipe which outputs the secondary air transmitted from the reheater, and wherein the three-way flow adjusting valve is arranged at a branch point where the bypass pipe and the dehumidified air pipe branch off or at a confluent point of the bypass pipe and the outlet pipe.
 6. A refrigeration air dryer according to claim 4, wherein a refrigeration bypass pipe bypassing the reheater is connected to a high-temperature refrigerant pipe connecting the refrigerant compressor and the reheater and an intermediate refrigerant pipe connecting the reheater and the condenser, and wherein the three-way flow adjusting valve is arranged at a branch point where the refrigeration bypass pipe and the high-temperature refrigerant pipe branch off or at a confluent point of the refrigerant bypass pipe and the intermediate refrigerant pipe. 